Question: Subtract.
There are many ways to solve this problem. Let's see two ways we can solve it. Place Value We can think in terms of hundredths: $\begin{aligned} &\phantom{=}31.2 - 22.31\\\\ &=31.20 - 22.31\\\\ &=3{,}120\text{ hundredths} - 2{,}231\text{ hundredths}\\\\ &=889\text{ hundredths}\\\\ &=8.89 \end{aligned}$ Place value table Let's line up the numbers by their decimal places. Tens Ones $.$ Tenths Hundredths ${3}$ ${1}$ $.$ ${2}$ $0$ $2$ $2$ $.$ ${3}$ $1$ Now, let's subtract each place value column. Tens Ones $.$ Tenths Hundredths $\overset{2}{\cancel{3}}$ $\overset{10}{\cancel{1}}$ $.$ $\overset{11}{\cancel{2}}$ $\overset{10}{\cancel{0}}$ $-$ $2$ $2$ $.$ ${3}$ $1$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $8$ $.$ $8$ $9$ $8.89 = 31.2 - 22.31$